Microplana terrestris and Some Basic Flatworm Ecology

 

Microplana terrestris, Long Plantation, Filey

Terrestrial flatworms are a relatively understudied group, which perhaps first burst into the public spotlight in the 1990s with reports of the notorious non-native invasive New Zealand flatworm Arthurdendyus triangulates multiplying in certain parts of Britain, posing a risk to our earthworms. The species had in fact been recorded from Northern Ireland from the early 1960s, and is now established in Ireland, parts of Scotland and northern England. There are approximately 14 established species present within the UK, with as few as 4 believed to be native. 

One such species and to date the only species I have recorded locally is the native Microplana terrestris, which does not appear to be particularly widespread in the eastern part of Yorkshire. Interestingly it has a relatively wide global distribution, and as with other species is likely spread by humans, particularly in association with the horticultural trade. Very little is known about terrestrial flatworms in Britain, including in some cases even the basic ecological parameters of some species, such as diet. This species is considered to be both a predator and a scavenger on soft bodied invertebrates like earthworms, snails and slugs.

Flatworms inject powerful digestive enzymes into their prey from the gut, which quickly dissolves the preys tissue before it being sucked back into the flatworms digestive tract. The gut is interesting in these species, as it has many branches radiating throughout the body. This is important as Flatworms have no circulatory system and require nutrients to be spread to the extremities of the body. Also interestingly the mouth is the only opening in the body to or from the gut! A small hole below the head is used for breeding, as flatworms are hermaphrodites 

I am quite familiar with aquatic flatworms in Britain, like Dugesia which can be super abundant in some waterbodies. Although not aquatic terrestrial flatworms as would be expected of a moist, soft bodied, invertebrate show a clear preference for damp habitats. Microplana is nocturnal and appears to favour humid woodland floor habitats. Interestingly though the situations I usually find it in are in relatively dry but humid deadwood and leaf litter. Excessive moisture may lead to suffocation, freezing or fungal infection. The literature suggests it is a relatively widespread species across a number of habitat types. My findings to date too limited to add anything to this other than I find it is mixed deciduous woodland, in agricultural and sub-urban areas with no apparent ancient woodland association.      

Refs.

Jones D. H., 2005. Identification of British Land flatworms. British Wildlife 2005.